The present invention is directed to an X-ray source and, in particular, to an X-ray source device which generates stable, high intensity X-rays with long life.
High intensity X-ray source devices are particularly desirable for use in X-ray lithography and X-ray microscopy. When used in X-ray lithography, X-ray source devices are used during the production phase of semiconductor chips. Conventional X-ray sources such as electron bombardment sources, synchrotrons and laser-driven plasma devices have been investigated for use in X-ray lithography. In conventional electron bomdardment X-ray sources, characteristic X-rays are generated by bombarding a fixed or rotating water cooled target, such as an anode made from copper, molybdenum or other such metals, with an electron beam. Such a conventional electron bombardment device suffers from poor efficiency and low output power and high intensity X-rays cannot be produced.
The X-ray flux from synchrotrons is suitable for lithography, but synchrotrons are large, complex and expensive. Laser-driven plasma X-ray sources are promising, but the high power lasers which are required to achieve high conversion efficiencies are often large and expensive and vapors tend to block the X-ray emitting window of such devices.
Various other proposals have been put forth to provide high intensity X-ray sources for use in X-ray lithography and electron microscopy. For example, in an article entitled Pulsed Plasma Source for X-Ray Lithography found in SPIE Vol. 275 Semiconductor Microlithography VI (1981) at pages 52-54, a pulsed plasma X-ray source device which produces X-rays by heating a target material to temperatures of several million degrees centigrade is proposed. Such a device produces soft X-rays.
In an article entitled Flash X-Ray Microscopy found in Science Vol. 205, July 27, 1979 at pages 401-402, an X-ray tube is proposed which includes a discharge capillary for producing, by erosion of several monolayers of the capillary wall, adense, high-temperature plasma. The tube also contains a rod cathode for launching an intense electron beam into the plasma to enhance the soft X-ray emission thereof. Such a device is useful for wet-sample viewing.
In an article entitled Gas Plasmas Yield X-Rays for Lithography found in Electronics, Jan. 27, 1982 at pages 40-41, gas-puff or gas-jet plasma sources are proposed. Such gas-jet plasma sources work by forcing a gas through a special nozzle in short bursts. The nozzle "shapes" the gas into a hollow cylinder. The instant before the cylindrical shape dissipates, electrical energy stored in a capacitor bank discharges through the gas, causing it to implode about the cylinder's axis. The resulting engery monentarily transforms the gas into a compressed plasma, which emits X-rays at wavelengths determined by the composition of the gas.
Although conventional X-ray source devices exist in the art and newly developed X-ray source devices have been proposed, it is still desired to provide an improved X-ray source device which efficiently produces X-rays of high intensity, long life and stability.